What happened
On December 15, 2019, an Aircraft Parts & Development A-9, registration LV-CYX, was conducting a glider tow operation at the Uspallata airfield in Mendoza, Argentina. After approximately 15 minutes of flight, the pilot performed a low-altitude pass over the runway to release the tow rope. Following the release, the pilot transitioned into the landing pattern. During the base turn, the aircraft experienced a sudden increase in descent rate. The pilot attempted to recover by applying full power and pulling back on the controls, but the descent continued. As the aircraft approached the ground, the pilot reduced power. The right wing struck the terrain, causing the aircraft to skid 28 meters before coming to a stop. The impact caused the main landing gear to collapse and resulted in significant damage to the aircraft's ventral area and tail skid. No injuries were reported.
The investigation
The investigation examined the operational environment of the Uspallata airfield, which sits at a high elevation of 6,505 feet. Investigators analyzed how this altitude affects aircraft performance, noting that high-altitude operations reduce engine power in non-turbocharged piston engines and decrease air density, which directly reduces lift. The investigation also considered the complexities of mountain flying, including the lack of a natural horizon when flying below mountain peaks and the prevalence of sudden downdrafts. The pilot's actions during the landing pattern were also reviewed, specifically the decision to fly the initial approach at an altitude lower than the established 500-foot minimum for that aircraft type.
Findings
- The landing pattern was flown at an altitude below the established 500-foot minimum.
- The airfield's high elevation (6,505 feet) significantly degraded the aircraft's engine performance and aerodynamic lift.
- The aircraft experienced a loss of control due to a possible downdraft during the base turn, which could not be recovered because of the low altitude.
- The aircraft was in a low-speed stall condition at the time of impact.